Paint coatings are protective surface coatings applied to substrates and cured to form dry continuous films for decorative purposes as well as to protect the substrate. Consumer latex paint coatings are air-drying aqueous coatings applied primarily to architectural interior or exterior surfaces, where the coatings are sufficiently fluid to flow out, form a continuous paint film, and then dry at ambient temperatures to form continuous films. A paint coating is ordinarily comprised of an organic polymeric binder, pigments, and various paint additives. The polymeric binder acts as a fluid vehicle for the pigments and imparts rheological properties to the fluid paint coating. In dried paint films, the polymeric binder functions as a binder for the pigments and provides adhesion of the dried paint film to the substrate. The pigments may be organic or inorganic and functionally contribute to opacity and color in addition to durability and hardness. The manufacture of paint coatings involves the preparation of a polymeric binder, mixing of component materials, grinding of pigments in the polymeric binder, and thinning to commercial standards. High speed dispersers or dissolvers are used in the grinding step to disperse the pigments into the polymeric binder solution.
Most retail paint stores stock a wide variety of ready-mixed color pigmented latex paints for consumer use where the color pigments are dispersed into the paint during manufacturing at the paint plant. However, a significant proportion of color pigmented paint is custom tinted at the point of sale to match a particular non-standard color selected by the consumer. In essence, a tiny amount of concentrated tinting pigment colorant is added to a consumer white or pastel tinting base to obtain the desired custom made color. Typically a small fraction of a fluid ounce and as high as twelve ounces of one, two, or more, and typically three pigment colorant concentrations are added to one gallon of tinting base. The concentrated pigment colorants are thoroughly mixed into the white or pastel tinting base by vigorous automatic shaking or stirring to produce a customized tinted latex paint. Tinting bases comprise highly concentrated levels of pigment ground into grinding vehicle to provide a high PVC (pigment-volume-concentration) fluid pigment concentrate. The most common grinding vehicle used in tinting concentrates is a blend of ethylene glycol and water in conjunction with various surfactants. The effect of concentrated pigment colorants on the paint base can be considerable including paint viscosity changes, drying problems, and water sensitivity problems, which are problems frequently attributed to interaction of the ethylene glycol in the concentrated pigmented colorants and the paint base. Although ethylene glycol provides excellent compatibility for both oil and water based consumer paints with manageable rheology and good freeze-thaw stability, ethylene glycol unfortunately is a volatile solvent which produces concentrated pigment colorants with a high VOC on the order of about 3 to 5 pounds/gallon. VOC is a measure of volatile organic compounds in a paint composition according to U.S. EPA Rule 24. See also ASTM Manual Series MNL4 and ASTM D-3960 and ASTM D-2369-87. Ethylene glycol has been criticized recently as being a suspected toxic substance and/or an animal teratogen. The surfactant system conventionally used with the pigmented tinting concentrate colorants are primarily nonionic and amphoteric surfactants in combination with anionic surfactant. The primary nonionic surfactant is nonyl phenol ethoxylate which provides wetting, dispensing, and stabilization for the concentrated pigment colorant. However, nonyl phenoyl ethoxylate has been identified as a suspected toxic substance by being biodegradable to a toxic phenol by-product. Most of the low molecular weight polymers suggested or tried as replacement vehicles for ethylene glycol while maintaining the existing surfactant system have resulted in low rheology at low shear and dialatency at high shear. These problems caused mixing and dispensing problems due to poor compatibility between the vehicle carrier used and nonyl phenol ethoxylate surfactant.
Latex paints for the consumer market ordinarily are based on polymeric binders prepared by emulsion polymerization of ethylenic monomers. A significant source of residual odor in latex consumer paints is directly due to the coalescing solvent. One typical coalescing solvent ordinarily contained in commercial air dry latex paints is 2,2,4-trimethylpentanediol monoisobutyrate (Texanol). The odor associated with the gradual volatilization of this solvent is considered offensive to many consumers and quite often the odor lingers for days or weeks after the paint is applied and dried. Considerable research effort has been directed toward eliminating volatile organic compounds (VOC) from consumer paints and especially from latex paints to eliminate emission problems as well as the odor problems. Thus, an urgent need exists to eliminate consumer VOC problems with air dry decorative paints including zero VOC concentrated colorants for tinting the consumer paints.
The concentrated pigment colorants of this invention exhibit a highly desirable shear thinning rheological profile which essentially duplicates the existing commercial standard based on ethylene glycol. The environmental need to replace ethylene glycol was a difficult achievement since low molecular weight polymers selected to replace ethylene glycol resulted in low rheology profile at low shear end and dialetency at the high shear end of the rheology profile. This presents manufacturing problems as well as a major practical commercial problem in respect to dispensing the concentrated pigment colorants from existing dispensing machines in retail paint stores. Poor physical properties, unacceptable rheology and compatibility were problems primarily caused by poor compatibility of the vehicle carrier and existing surfactants based on nonyl phenol ethoxylate. British Patent No. 861,223 suggests pigment tinting compositions using certain glycols or polyoxyalkylene diols in association with non-ionic or anionic surface active agents as vehicles for the pigment.
It now has been found that organic solvent-free concentrated pigment colorants can be produced free of ethylene glycol and nonyl phenol ethoxylate surfactant, where such concentrated pigment colorants are compatible with current consumer latex paints or solvent paints as well as new experimental zero VOC, air dry latex paints. It has been found that certain narrow range, low molecular weight, polyethylene glycol polyethers in combination with a surfactant system based on alkyl polyglycoside non-ionic surfactant eliminate undesirable volatile organics while providing good pigment wetting, dispersing, and stability, along with good shear thinning rheology as well as long open dry times necessary to prevent nozzle blockage in dispensing canisters for the colorants at the point of sale. The low molecular weight polyether organic vehicle in conjunction with alkyl polyglycosides provides maximum flow, comparable theology and better open dry time relative to prior art systems based on ethylene glycol vehicle and nonyl phenol ethoxylated surfactant, and further eliminates organic solvent emission and toxicity problems while maintaining proper drying, wide range compatibility, and good pigment wetting, within water dispersible latex paints without causing a VOC problem. The concentrated pigment colorants are similarly compatible with existing consumer latex paints and solvent paints as well as existing ethylene glycol based pigment concentrates thereby eliminating change over problems and the need for stocking duplicate pigment concentrates. The concentrated pigment colorants of this invention are easy to manufacture and are particularly suitable for dispensing through existing open nozzle canister dispensing machines. The concentrated pigment colorant of this invention advantageously minimizes toxicity, eliminates organic solvent emissions, exhibits proper humectency and hygroscopicity to insure proper drying as well as compatibility with existing water dispersed or solvent dispersed paints, good pigment wetting and dispersibility from current dispensing devices without contributing to VOC. These and other advantages will become more apparent by referring to the detailed description and illustrative examples of the invention.